Traditionally, in order to estimate the location of a mobile telecommunications unit (xe2x80x9cmobilexe2x80x9d), such as a cellular phone, a laptop computer, a personal digital assistant or the like, the mobile needs to receive and decode signals from four distinct Global Positioning System (xe2x80x9cGPSxe2x80x9d) satellites. These signals contain two sources of information from which a mobile""s location can be computed: 1) pseudo-ranging information; and 2) the satellites"" ephemeris. Pseudo-ranging information is used to compute the time difference of arrival of the signals from the satellites to a destination (in this case, the mobile). The satellites"" ephemeris comprises information about the exact locations of the satellites in space, typically compiled in a tabular format. With these two sources of information, it is possible to determine the location of a mobile using a triangulation technique.
There exists IS-95 based WAG systems which provide location predictions with a high level of accuracy (e.g., within about 15 feet). Such WAG systems take advantage of the fact that there are GPS receivers in IS-95 base stations, which have radio connections to mobiles, and in MSCs for synchronization purposes. These same GPS receivers are used by WAG systems to reduce the time required to determine the location of a mobile. The primary goal of WAG is to reduce the processing and computing load on a mobile. This goal is met by removing the need for the mobile to process or compute pseudo-ranging information and ephemeris information contained in a GPS signal. To accomplish this, a WAG server is placed in a MSC accompanied by a full GPS receiver to perform the bulk of the signal processing and computation. Assuming the MSC to which the mobile is connected can receive signals from the same satellites as the mobile because of its proximity to the mobile (e.g., less than 100 km), the MSC can tell the four satellites, from among twenty-four GPS satellites, to which the mobile needs to tune. This information significantly reduces the time required for the mobile to search for visible satellites. Furthermore, since the MSC""s GPS receiver is capable of decoding pseudo-ranging and ephemeris information, it is not necessary for the mobile to process this information, thus reducing the processing load on the mobile. This reduction in processing load on mobiles allows for the use of simplified GPS receivers in WAG-capable mobiles.
The present invention concerns the determination of a mobile""s location in a UMTS network. UMTS is a third-generation wireless system which is designed to support high-data-rate multimedia services. However, in a UMTS network, the base stations are not synchronized. This means that GPS receivers are not required for the operation of a UMTS. The lack of GPS receivers complicates the implementation of WAG-like services in a UMTS network. One way of providing WAG-like services in a UMTS would be to add GPS receivers to MSCs in a UMTS landline network. However, this solution would significantly increase the overall cost of the system.
Accordingly, it is desirable to provide methods and systems for implementing WAG-like services in UMTS networks that do not require the addition of traditional GPS receivers.
The present invention provides methods and systems for determining the location of mobiles in a telecommunications system. More specifically, the present invention comprises methods and systems for locating a mobile within a UMTS network. According to embodiments of the present invention, a UNAG server is deployed within a UMTS landline network and is adapted to provide WAG-like services to mobiles comprising simplified GPS receivers. The UNAG server contacts a GPS Master Control Station (MCS), such as the one located in Colorado Springs, Colorado, to obtain orbital positioning information on all GPS satellites. When a mobile requests information about its location, the UNAG server processes the orbital positioning information to determine which four GPS satellites should be visible to the mobile. The UNAG server then transmits tuning information associated with the four satellites to the mobile, which enables the mobile to receive GPS information from the four satellites. Next, the mobile decodes pseudo-ranging information from within the GPS information and transmits it to the UNAG server. The UNAG server processes the pseudo-ranging information associated with the mobile along with the previously calculated positions of the four satellites to calculate the geographic location of the mobile. Finally, the UNAG server transmits location information back to the mobile.